Sequence and Characterization of the HoxA7 Gene. The Hox A7 gene is a mouse gene characterized by the presence of a homeobox region typical of the Antennapedia class of proteins found in Drosophila. Starting with a clone derived from mouse genomic DNA, the complete sequence of the structural gene, as well as upstream and downstream regulatory regions, were determined. A variety of studies have led to the assignment in this sequence of the probable transcription start site as well as likely regions for the interaction with proteins that regulate transcription. Site-specific Mutagenesis of Presumptive ATP Binding Sites in Escherichia coli Adenylyl Cyclase. The region of the enzyme bounded by Alanine 190 and Arginine 197 was studied as a probable region for substrate binding. Site-directed mutagenesis was carried out on Lysine 196 by replacing this residue with a variety of other amino acids. It was found that replacement with other basic amino acids led to retention of some activity, while replacement with other classes of amino acids generally led to abolition of activity. The conclusion from these studies is that the charge in the vicinity of Lysine 196 is crucial for enzymatic activity. Sequence and Organization of a Monocistronic ptsH Operon in Mycoplasma. A sequencing project, designed to isolate genomic clones for the enzymes of the transport system known as the phosphoenolpyruvate: sugar phosphotransferase system (PTS), was undertaken. Several clones were isolated that allowed the determination of the sequence of the gene encoding the PTS phosphocarrier protein known as Hpr as well as of flanking regions upstream and that the gene encoding Hpr (the ptsH gene) was located in an operon that is monocistronic. This is in marked contrast to the organization of all previously sequenced ptsH genes in other organisms where the ptsH gene is found in a polycistronic operon.